Laminated resin interior are obtained by applying on the wall of a mold having the required shape mechanically resistance fibers coated with a resin. The result would be a wall in contact with the mold having surface irregularities and the mechanically resistant wall obtained would include pores, which would favour the penetration of water within the thickness of the wall, thereby degrading the constituent resins.
In order to provide a good appearance to the surface of laminated castings, it is known first to coat the surface of the mold with a film forming resin, technically called gel coat. The film forming resins used are polyesters, epoxy resins, etc., which provide semi-permeable membranes. The result is that when they are applied on laminated resin walls that remain in contact with water, such as swimming pool walls and boat hulls, the outer layers of the gel coat allow the water to penetrate rather quickly into the laminated resin, thereby causing partial separations of the resin layer of the gel coat and the formation of bubbles or blisters. This phenomenon, known as "blistering", lets the water flow to the laminate which is subjected to hydrolysis, so that in addition to the unaesthetic appearance of the blisters, the mechanical characteristics of the laminate are reduced.
In an effort to remedy this disadvantage, it has been proposed to interpose between the laminate and the superficial resin layer or gel coat a layer of resin forming a barrier against the water, called "skin coat". Such a use of two superimposed layers in a laminate limits the choice of the barrier-layer resin, which has to be compatible in order to avoid in particular a risk of separtion between the successive layers, particularly under the effect of impacts, as is the case with an intermediate layer of epoxy resin.
So, it has been proposed to provide such a barrier-layer of a vinylester based resin. The use of vinylester based resins, which has been known for a long time in the polyester industry for increasing corrosion resistance, provides a certain increase of the resistance to the penetration of water, while maintaining or even increasing the mechanical strength of the laminate thus coated.
However, it has been recognized that the vinylester based barrier-layer exhibits a certain degree of sensitivity to water and does not delay in a satisfactory way the hydrolysis of the resin of the laminate.
Due to the known high anti-corrosion characteristics of the vinylester resins, the inventor has been led to think that the part played by the barrier against the penetration of water was not tied to the anticorrosive properties of the resin constituting the layer, but resulted from a purely mechanical effect. The vinylester resins which have reactive sites only at the end of their chain, provide in fact a network with a small steric space requirement, thereby facilitating the passage of water through them.
On the basis of this theory, the inventor has studied the behaviour as barrier-layer between the gel coat and the laminate of resins having a high steric space requirement, and he has established that a high steric space requirement would greatly reduce the layer permeability.